Zytiga (abiraterone) vs Xtandi (enzalutamide) for advanced prostate cancer

Background

Prostate cancer feeds on male hormones.

The main male hormone is testosterone.

Below I use 'testosterone', but I mean all the male hormones.

Primary hormone therapy

When it becomes clear that your first treatment (surgery or radiation) was not enough, your doctor will often start primary hormone therapy.

Primary hormone therapy often uses one of these or a similar injection, usually monthly or 3 monthly:

Zoladex (Goserelin), Lupron (leuprorelin), Eligard (leuprolide), Lucrin (leuprorelin acetate),  Suprefact/Suprecor (buserelin), Synarel (nafarelin), histrelin (Supprelin), Suprelorin/Ovuplant (deslorelin), Triptorelin (diphereline), Firmagon (degarelix)

These work by stopping your testes (balls) from producing testosterone.

Your pituitary gland sends messages to your balls to make testosterone.

Firmagon (degarelix) works directly in the pituitary gland to stop it from sending messages to your balls to make testosterone.

All the others work by having the brain send messages to the pituitary gland to stop it from sending messages to your balls to make testosterone.

Sometimes (perhaps if you are frail) tablets are used:

Casodex, Cosudex (bicalutamide), Nilandron, Anandron (nilutamide), Eulexin (flutamide)

These work inside the prostate cancer to stop it using any testosterone that may still be in your blood.

Secondary hormone therapy

When it becomes clear that your primary hormone therapy is not enough, your doctor will usually add secondary hormone therapy tablets.

There are a number of secondary hormone therapy drugs (see below) but at the time of writing (2 June 2021) the most commonly used, and the ones we have the most evidence for, are Xtandi (enzalutamide) and Zytiga (abiraterone). These two are essentially free to Australian men on the PBS and usually covered by insurance in the USA.

An earlier rule that you had to have Taxotere (Docetaxel) before you got these has been cancelled.

Xtandi (enzalutamide) works inside the prostate cancer to prevent the prostate cancer using any testosterone it comes across in the blood.

Zytiga (abiraterone) works in the blood by gathering up the chemicals that can be turned into testosterone by your balls, adrenal glands, or even the prostate cancer itself.

Neither drug is a magic bullet. They don't work in every man. They don't work forever.

It seems to me that they have about the same results, so doctors look at any health problems you may have that that drug may make worse:

Xtandi (enzalutamide)

You and your doctor will avoid if you have:

• History of falls, unsteady gait (walk)

• Neurological issues

• Significant fatigue when you are about to start the drug

• Mild pain when about to start the drug

• Polypharmacy (lots of medicines for other conditions)

Zytiga (abiraterone)

You and your doctor will avoid if you have:

• Congestive heart failure before you start the drug.

• Edema (swelling, from small to all) before you start the drug

• Renal impairment (kidneys don't work well)

• Diabetes

Both Zytiga (abiraterone) and Xtandi (enzalutamide) together?

• You don't last any longer.

• You have more side effects, and more serious side effects.

Neither

If a blood test shows you have AR-V7 in your blood:

• Neither Zytiga (abiraterone) nor Xtandi (enzalutamide) are likely to work.

• Chemotherapy drugs will work much better for you.

Steroids

• Corticosteroids must be taken with Zytiga (abiraterone)

• Corticosteroids can be taken with Xtandi (enzalutamide) to ease side effects of severe fatigue and loss of appetite.

• Corticosteroid tablets include prednisolone, dexamethasone and several others.

Other drugs that work in the prostate cancer in a similar way to Xtandi (enzalutamide):

• Nubeqa (Darolutamide)

• Erlyand in Australia, Erleada in USA (Apalutamide)

Another drug that works in the blood in a similar way to Zytiga (abiraterone):

• Nizoral (Ketoconazole)